1. Technical Field
The instant invention relates to unique polymeric bicomponent fibers and to the production of wicking devices, especially, nibs and ink reservoirs for writing and marking instruments made from such fibers. More specifically, this invention is directed to the production and use of nibs and ink reservoirs, particularly nibs for writing and marking instruments such as fiber tip pens and “felt tip” markers, as well as roller ball wicks for roller ball pens, wherein the wicking devices are formed of sheath-core, melt blown, bicomponent fibers wherein a core of a nylon 6,6 is substantially fully covered with a sheath of polyethylene terephthalate or a copolymer thereof. For the production of nibs, the core material may be polybutylene terephthalate.
2. Discussion of the Prior Art
The production of thermally bonded fibrous products for various applications is disclosed in commonly assigned U.S. Pat. No. 5,607,766 issued Mar. 4, 1997 (the subject matter of which is incorporated herein in its entirety by reference) (the '766 patent) using bicomponent fibers comprising a coating of a polyester sheath, such as polyethylene terephthalate and its copolymers, over a thermoplastic core, such as polypropylene and polybutylene terephthalate. There are currently commercial permanent ink markers using nibs made of polyester felt impregnated with phenolic resin which have an aggressive xylene-based ink formulation. Past attempts to produce nibs formed of bonded polyester fiber tows, particularly for use with writing and marking instruments incorporating such aggressive inks, have suffered unacceptable “drainback” properties. A drainback test is where the marker is stood on end, tip up, for 48 hours. It is then inverted (tip down). The pen must write on the third stroke to pass the test. While currently available polyester felt/phenolic nibs satisfy commercial drainback criteria, early polyester filament-based attempts to reproduce these properties failed.
Although core materials of polybutylene terephthalate, as disclosed in the '766 patent, show desirable properties for use as reservoirs in writing and marking instruments and the polyester/polypropylene bicomponent fiber products discussed therein are acceptable for selected applications, both polypropylene and nylon 6 core materials in polyester sheath bicomponent fiber thermally bonded writing and marking instrument components have now been found to unduly soften in the presence of certain particularly aggressive ink formulations, making marking and writing instrument components, particularly nibs, formed of bicomponent fibers having polyester sheaths with such core polymers of limited utility and, from a commercial standpoint, effectively useless.
This invention relates to the surprising discovery that, in the production of nibs for writing instruments, such as roller ball or fiber-point pens, or marking instruments, such as felt-tipped permanent highlighters, dry-erase markers and the like, especially those incorporating aggressive inks such as xylene-based permanent ink formulations, the use of a bonded fibrous element formed from melt blown bicomponent fibers comprising a polyester sheath and a nylon 6,6 or polybutylene terephthalate core material provides excellent drainback and ink laydown properties, thermal stability and physical robustness. Use of bonded fiber tow materials, even bicomponent fiber tows having a polyester sheath over a nylon 6,6 core, will fail the drainback test, but melt blown bicomponent fibers of these polymers produce acceptable nibs for writing and marking instruments.
Such products also have unexpectedly improved solvent resistance and increased stiffness avoiding degradation under pressure in use. Moreover, these unique bicomponent fibers produces writing and marking instrument components which are less expensive than competitive products, such as the polyester felt/phenolic nibs currently in the market. Similar advantages are expected for ink reservoirs formed of melt blown polyester/nylon 6,6 bicomponent fibers.